1. Field of the Invention
The present invention relates to an end structure for a synthetic resin member such as a molding, and in particular to an end structure for a synthetic resin member of a type wherein the end structure is integrally formed by injection on the synthetic resin member.
2. Description of the Related Art
Referring to FIGS. 4 to 10, conventional end structures for synthetic resin member are summarized.
An end structure integrally formed by injection at the end of a synthetic resin member such as a molding, as disclosed in Japanese Utility Model Publication of Unexamined Application No. SHO-55-151857, is commonly known.
In order to make this end structure, an end surface 2 of a molding 1, which is a synthetic resin member is formed in a flat shape perpendicular to the longitudinal direction of the molding 1 as shown in FIG. 4. On the outside of the end surface 2 a terminal or end structure 3 is integrally formed by injection.
In the method of integrally forming the molding end structure 3, the end section of the molding 1 is interposedly supported between a pair of vertical injection molds 5, 7 as in FIG. 5. Molten synthetic resin is pressure injected in the direction of the arrow in FIG. 5 from an injection port 6 in the upper mold 5 into a molding chamber 8 defined by the end surface 2 of the molding 1 and the inner surfaces of the upper mold 5 and the lower mold 7. Accordingly, the end structure 3 is integrally formed in a desired form on the end surface of the molding 1.
In addition, in Japenese Utility Model Publication of Unexamined Application No. SHO-59-35250, an indented portion 13 is formed on a flat end surface 12 of a molding 11 at right angles to the longitudinal direction of the molding 11 as shown in FIG. 7. Then, an end structure 14 is integrally formed on the end portion of the molding 11, by injection into a molding chamber 18 in FIG. 8.
The end structure 14 of the molding 11 is constructed by pressure injection of molten resin, as shown by the arrow in FIG. 8, from an injection port 16 in a top mold 15, into the molding chamber 18 which is defined by the inner surface of an upper die 15 and a lower die 17 and a flat end surface 12 of the molding 11. The molten resin is caused to flow as far as the indented portion 13 so that the end structure 14 is firmly secured to the end portion of the molding 11.
Furthermore, in Japanese Utility Model Publication of Unexamined Application No. SHO-55-91342, an end structure 23 containing an indented portion 24 in the mounting surface side (the top surface in FIG. 9) of a molding 21, which can be for a vehicle body or the like, is integrally formed on a flat end surface 22 of the molding 21 by injection molding as shown in FIG. 10.
The end structure 23 of the molding 21 is interposedly supported by an upper die 25 and a lower die 27. Molten resin is pressure injected, as shown by the arrow in FIG. 10, from an injection port 26 in a top mold 25, into a molding chamber 28 which is defined by the inner surfaces of an upper die 25 and a lower die 27 and a flat end surface 22 of the molding 21. Accordingly, the end structure 23 is integrally formed at the end of the molding 21. In this example, a projecting portion 25A is formed on the inside of the upper die 25 so that the indented portion 24 is formed after molding on the mounting surface side (the upper side in FIG. 9) of the end structure 23.
However, in the conventional structures as shown in FIG. 4 to FIG. 6, the end structure 3 is integrally molded by injection onto the flat end surface 2 of the molding 1 which is a synthetic resin member, so that for the welding area between the flat end surface 2 and the end structure 3 of the molding 1, there is only a narrow area which coincides with the cross sectional area of the molding 1. Adequate strength of weld is therefore not obtained at that welded portion. Accordingly, the end structure 3 will on occasion separate from the end surface 2 after welding. Furthermore, the end structure 3 is solidly formed with a thick body, so a large volume of the molten resin material is required for injection into the molding chamber 18. As a result, after molding, a shrinkage cavity 4 is readily produced in the surface of the end structure 3, so there is the drawback that the outward appearance of the entire body of the molding 1, including the end structure 3, is unsatisfactory.
Also, in the examples of conventional end structures shown in FIG. 7 and FIG. 8, an indented portion 13 is formed in the end surface 12 of the molding 11, so that when the end structure 14 is integrally formed by injection on the end surface of the molding 11 the molten resin from which the end structure 14 is formed flows simultaneously into the indented portion 13 to form an integral body. Accordingly, the welded area between the end surface 12 and the end structure 14 of the molding 11 increases and the welding strength increases. However, because the end structure 14 is solid and thick-bodied and is formed by pressure injection of a large volume of molten resin, a shrinkage cavity is produced on the surface of the end structure 14 after molding as with the conventional example shown in FIG. 4 to FIG. 6, so the drawback occurs that the outward appearance is unsatisfactory.
Furthermore, in the conventional examples shown in FIG. 9 and FIG. 10, the indented portion 24 is formed on the mounting surface side (the top in FIG. 9) on the end structure of the molding 21 for a vehicle or the like, so that the amount of molten resin material required to form the end structure 23 is reduced, and the body thickness of the end structure is also reduced. As a result, the formation of the shrinkage cavity in the surface is prevented. However, after the end structure 23 is molded, a tip portion 23A is inclined to be distorted from the regular shape shown by the solid line 23A to the shape indicated by the dotted line 23AA in FIG. 9. The drawback occurs that the molding, especially in the status of the mounted end structure 23 and its outward appearance, is unsatisfactory.